Ian,
Just re-install the 4.1 player. There may be other files or dll's involved for proper playback. I only un-register the qidvdf.ax filter when I want the system to use some other decoder such as WinDVD's. There are times when, after filter juggling, even after I re-register the qidvdf filter that the system will not play HD files full speed (as if the hardware acceleration has been turned off). If that happens, I run the 4.1 update installer program and select 'Repair' installation to get it back working right. I'm also using the 7093 display drivers. I haven't tried any of the newer ones.
I mainly only use Graphedit as a tool to just show me what filters are going to be automatically grabbed if I run a player such as Windows Media Player (or Zoom). It should show the playback file connected to the MPEG2 Splitter, then the Cinemaster decoder followed by the Overlay2 mixer, and then the Video renderer. Make certain you don't have the Elecard de-muxer register or it will use that instead of the MPEG2 Splitter and all you will get is a black screen.
Zoom Player is great to use with the ATI player installation because it has all the aspect ratio controls which the ATI player lacks.
Gary